Compound section structural means with connecting insulators are suitable for the manufacture of frames in which outer portions, for example composed of a light metal, are interconnected by means of an insulator of foamed or expanded synthetic resin material.
Frames of this kind are suitable for windows, doors, facade sections and the like, in which it is vital to prevent or to impede heat flow, resulting from temperature differentials, through the frame.
It is known to press bars made of a synthetic resin with snap action into prepared cavities provided in the surfaces of the metal sections to be interconnected and thus to insert a third member of a suitable strength and adequate holding properties between the parts to be interconnected. In this method however, it is difficult to obtain predetermined tolerances, since it is practically impossible to bring about an interconnection of the frames which is free from play.
It is also known that attempts have been made to remove these difficulties by manufacturing the two outer portions of the frame initially as a solid unit and to form a cavity between these two portions. This cavity is then filled with a liquid synthetic resin. When the synthetic resin has hardened, the wall of the cavity is cut through by mechanical means and the direct metallic connection between the two frame halves is thus removed. While predetermined tolerances are maintained by this measure, since a firm interconnection of the sections can be obtained by the poured-in synthetic resin which subsequently hardens, it is difficult for the unwanted cavity walls to be removed simply and cheaply, since it has been found in practice that the skin on the surface of the synthetic resin body is damaged by mechanical cutting operations and its strength is thus reduced. Moreover, damage to the surface of the insulator involves the danger of a premature ageing resulting from detrimental influences of moisture, vapors and the like.